A very thoughtful response. PSK31 is one of my favourite modes. I
have used several different xcvrs ... at the moment I am using a
monitor. As you point out the signal must be kept below S9 in the
transmitted signal. I did the tests into a dummy load. The TS-50 is
primarily designed as a mobile SSB xcvr ... however I find it
output. Beyond the level the IMD figures drop rapidly. I generally
anyone I hear ... including a lot of DX (with my rotatable dipole at
I expect the KX3 will work vy well at 5 watts output. When the KXPA3
>The question and response below only consider thermal limitations. There
>are also signal quality limitations in some data modes, PSK31 in particular.
>
>PSK31 is very intolerant of non-linearity. The "crest factor" of
>PSK31 can be up to 2, i.e. the peak power can be twice the average
>power. Since it is clipping of the peaks that causes splatter or IMD,
>with most transmitters you need to keep the output power below one-half
>the rated maximum in order to ensure linearity. Linearity is not nearly
>as much of a problem in RTTY, but it matters in PSK31.
>
>If you have the means to measure IMD of your transmitted PSK31 signal,
>you can test this. A couple of years ago I did some tests using a
>"PSKmeter" (a device that monitors a transmitted PSK31 signal and
>reports the level of IMD products in the signal) observing the output of
>my K3 in PSK31 with the K3 in DATA A mode. What I found was that IMD
>levels were low at powers below 5 watts (KPA3 not in line) and at powers
>above 12 watts but below 50 watts (KPA3 in line), but as the power was
>increased above the 5 watt or 50 watt level, the measured IMD started to
>increase quite rapidly. The reported IMD at full power (10 watts without
>the KPA3 or 100 watts with the KPA3) was high - much higher than I would
>consider acceptable.
>
>I did not do similar tests in the K3's PSK D mode, but I have no reason
>to believe they would be better. See W7AY's measurements of PSK31
>quality in PSK D vs. DATA A (for power levels below 5W and 50W) at
><
http://homepage.mac.com/chen/Technical/K3/Digital/digital.html>.
>
>I would suggest to anyone who plans to transmit PSK31 at powers greater
>than the recommended 5 watt (one-half full power) level that they should
>monitor the quality of their transmitted signal to ensure that the
>signal quality is acceptable. The simplest "low tech" way to do this is
>to have another station report IMD figures for your signal at various
>power levels. Note that the other station should be located such that
>the signal they receive from you is neither too strong (a very strong
>signal can produce IMD in the receiver) nor too weak (the signal must be
>well above the noise level for the reported IMD measurement to be
>meaningful).
>
>In RTTY such precautions do not appear to be necessary. Qualitative
>observations of the spectrum of my K3's RTTY signals in both FSK D and
>AFSK A modes did not show a significant observable difference between
>the signals at 50 watts and the signals at 100 watts.
>
>73,
>Rich VE3KI
>
>
>Wayne Burdick wrote:
>
> > Jim Dunstan wrote:
> >
> >> The KX3 specifications indicate a nominal 10 watts output. When
> >> operating a mode such as PSK, which presents a continuous output,
> >> what is the recommended power output?
> >
> > We recommend using 5 W for data modes and keeping transmissions
> > reasonably short. However, you can definitely use full power (up to 12
> > W) if the duty cycle is low, such as during hunt-and-pounce in a
> > contest. Of course as the duty cycle goes up, so will the PA and case
> > temperature, and eventually the KX3 may automatically roll back your
> > power output.
> >
> > I just did a test using the built-in PSK-D mode, alternately
> > transmitting and receiving for 20 seconds each (simulating short
> > contest contacts). At 12 watts (20 meters), the temperature never got
> > high enough to roll back power during ten minutes of this.
> >
> > I then tested the KX3's high-efficiency TX mode, which reduces current
> > drain by roughly 50% for a given power level. This mode kicks in at at
> > 5.0 W or less in CW/FSK-D modes, and at 3.0 W or less in all other
> > modes. So I set power to 3.0 W in PSK-D mode, which is amazingly
> > effective given the S/N ratio of PSK31, and transmitted continuously.
> > After 5 minutes the PA temperature was still increasing slowly, but
> > I'm guessing I could have gone on for another 5-10 minutes.
> >
> > The lesson, here, is to let the other station transmit once in awhile :)
> >
> > Wayne
> > N6KR
>
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